1. Field of the Invention
The present invention relates generally to arc lamps, and more particularly, arc lamps of the type which have short arc gaps.
2. Description of the Prior Art
It is well-known to utilize lamps having short arc gaps to provide intense point sources of light for applications such as instrumentation and projection. More specifically, it is well known to utilize short arc lamps in medical endoscopes, which serve as illuminators of fiber optic bundles that allow visual examination of body canals and adjacent organs without conventional surgery. Short arc lamps are also used in industrial endoscopes to examine structures and components difficult to inspect visually, such as the interiors jet engines. Generally speaking, such lamps include a sealed concave chamber which contains a gas pressurized to several atmospheres, an anode and cathode which are mounted along the central axis of the concave chamber to define an arc gap, and a window at the mouth of the chamber to permit transmission of light generated by electrical discharge across the arc gap. It is known that the lamp body can be formed of an opaque cylinder of ceramic material and that the concave chamber can be formed in one end of the cylinder by a mandrel or the like.
In such prior arc lamps, the temperatures generated within the lamps may be quite high, sometimes exceeding 600.degree. C. Because the temperatures at the exterior of the lamp are substantially lower, large temperature gradients exist through the lamp body. One result of such temperature gradients in prior art lamps has been cracking of the ceramic body or of the reflector surface especially if the lamps are used at high wattages, say above 800 watts. Such cracking can cause discontinuities or discolorations in the reflective surface of the lamp, thereby diminishing the effectiveness of the lamp as an illuminator. In addition, such cracking can lead to potentially explosive conditions.